/*
      i2c-stub.c - I2C/SMBus chip emulator
  
      Copyright (c) 2004 Mark M. Hoffman <mhoffman@lightlink.com>
      Copyright (C) 2007-2014 Jean Delvare <jdelvare@suse.de>
  
      This program is free software; you can redistribute it and/or modify
      it under the terms of the GNU General Public License as published by
      the Free Software Foundation; either version 2 of the License, or
      (at your option) any later version.
  
      This program is distributed in the hope that it will be useful,
      but WITHOUT ANY WARRANTY; without even the implied warranty of
      MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
      GNU General Public License for more details.
  */
  
  #define DEBUG 1
  
  #include <linux/init.h>
  #include <linux/module.h>
  #include <linux/kernel.h>
  #include <linux/slab.h>
  #include <linux/errno.h>
  #include <linux/i2c.h>
  #include <linux/list.h>
  
  #define MAX_CHIPS 10
  
  /*
   * Support for I2C_FUNC_SMBUS_BLOCK_DATA is disabled by default and must
   * be enabled explicitly by setting the I2C_FUNC_SMBUS_BLOCK_DATA bits
   * in the 'functionality' module parameter.
   */
  #define STUB_FUNC_DEFAULT \
  		(I2C_FUNC_SMBUS_QUICK | I2C_FUNC_SMBUS_BYTE | \
  		 I2C_FUNC_SMBUS_BYTE_DATA | I2C_FUNC_SMBUS_WORD_DATA | \
  		 I2C_FUNC_SMBUS_I2C_BLOCK)
  
  #define STUB_FUNC_ALL \
  		(STUB_FUNC_DEFAULT | I2C_FUNC_SMBUS_BLOCK_DATA)
  
  static unsigned short chip_addr[MAX_CHIPS];
  module_param_array(chip_addr, ushort, NULL, S_IRUGO);
  MODULE_PARM_DESC(chip_addr,
  		 "Chip addresses (up to 10, between 0x03 and 0x77)");
  
  static unsigned long functionality = STUB_FUNC_DEFAULT;
  module_param(functionality, ulong, S_IRUGO | S_IWUSR);
  MODULE_PARM_DESC(functionality, "Override functionality bitfield");
  
  /* Some chips have banked register ranges */
  
  static u8 bank_reg[MAX_CHIPS];
  module_param_array(bank_reg, byte, NULL, S_IRUGO);
  MODULE_PARM_DESC(bank_reg, "Bank register");
  
  static u8 bank_mask[MAX_CHIPS];
  module_param_array(bank_mask, byte, NULL, S_IRUGO);
  MODULE_PARM_DESC(bank_mask, "Bank value mask");
  
  static u8 bank_start[MAX_CHIPS];
  module_param_array(bank_start, byte, NULL, S_IRUGO);
  MODULE_PARM_DESC(bank_start, "First banked register");
  
  static u8 bank_end[MAX_CHIPS];
  module_param_array(bank_end, byte, NULL, S_IRUGO);
  MODULE_PARM_DESC(bank_end, "Last banked register");
  
  struct smbus_block_data {
  	struct list_head node;
  	u8 command;
  	u8 len;
  	u8 block[I2C_SMBUS_BLOCK_MAX];
  };
  
  struct stub_chip {
  	u8 pointer;
  	u16 words[256];		/* Byte operations use the LSB as per SMBus
  				   specification */
  	struct list_head smbus_blocks;
  
  	/* For chips with banks, extra registers are allocated dynamically */
  	u8 bank_reg;
  	u8 bank_shift;
  	u8 bank_mask;
  	u8 bank_sel;		/* Currently selected bank */
  	u8 bank_start;
  	u8 bank_end;
  	u16 bank_size;
  	u16 *bank_words;	/* Room for bank_mask * bank_size registers */
  };
  
  static struct stub_chip *stub_chips;
  static int stub_chips_nr;
  
  static struct smbus_block_data *stub_find_block(struct device *dev,
  						struct stub_chip *chip,
  						u8 command, bool create)
  {
  	struct smbus_block_data *b, *rb = NULL;
  
  	list_for_each_entry(b, &chip->smbus_blocks, node) {
  		if (b->command == command) {
  			rb = b;
  			break;
  		}
  	}
  	if (rb == NULL && create) {
  		rb = devm_kzalloc(dev, sizeof(*rb), GFP_KERNEL);
  		if (rb == NULL)
  			return rb;
  		rb->command = command;
  		list_add(&rb->node, &chip->smbus_blocks);
  	}
  	return rb;
  }
  
  static u16 *stub_get_wordp(struct stub_chip *chip, u8 offset)
  {
  	if (chip->bank_sel &&
  	    offset >= chip->bank_start && offset <= chip->bank_end)
  		return chip->bank_words +
  		       (chip->bank_sel - 1) * chip->bank_size +
  		       offset - chip->bank_start;
  	else
  		return chip->words + offset;
  }
  
  /* Return negative errno on error. */
  static s32 stub_xfer(struct i2c_adapter *adap, u16 addr, unsigned short flags,
  	char read_write, u8 command, int size, union i2c_smbus_data *data)
  {
  	s32 ret;
  	int i, len;
  	struct stub_chip *chip = NULL;
  	struct smbus_block_data *b;
  	u16 *wordp;
  
  	/* Search for the right chip */
  	for (i = 0; i < stub_chips_nr; i++) {
  		if (addr == chip_addr[i]) {
  			chip = stub_chips + i;
  			break;
  		}
  	}
  	if (!chip)
  		return -ENODEV;
  
  	switch (size) {
  
  	case I2C_SMBUS_QUICK:
  		dev_dbg(&adap->dev, "smbus quick - addr 0x%02x
  ", addr);
  		ret = 0;
  		break;
  
  	case I2C_SMBUS_BYTE:
  		if (read_write == I2C_SMBUS_WRITE) {
  			chip->pointer = command;
  			dev_dbg(&adap->dev,
  				"smbus byte - addr 0x%02x, wrote 0x%02x.
  ",
  				addr, command);
  		} else {
  			wordp = stub_get_wordp(chip, chip->pointer++);
  			data->byte = *wordp & 0xff;
  			dev_dbg(&adap->dev,
  				"smbus byte - addr 0x%02x, read  0x%02x.
  ",
  				addr, data->byte);
  		}
  
  		ret = 0;
  		break;
  
  	case I2C_SMBUS_BYTE_DATA:
  		wordp = stub_get_wordp(chip, command);
  		if (read_write == I2C_SMBUS_WRITE) {
  			*wordp &= 0xff00;
  			*wordp |= data->byte;
  			dev_dbg(&adap->dev,
  				"smbus byte data - addr 0x%02x, wrote 0x%02x at 0x%02x.
  ",
  				addr, data->byte, command);
  
  			/* Set the bank as needed */
  			if (chip->bank_words && command == chip->bank_reg) {
  				chip->bank_sel =
  					(data->byte >> chip->bank_shift)
  					& chip->bank_mask;
  				dev_dbg(&adap->dev,
  					"switching to bank %u.
  ",
  					chip->bank_sel);
  			}
  		} else {
  			data->byte = *wordp & 0xff;
  			dev_dbg(&adap->dev,
  				"smbus byte data - addr 0x%02x, read  0x%02x at 0x%02x.
  ",
  				addr, data->byte, command);
  		}
  		chip->pointer = command + 1;
  
  		ret = 0;
  		break;
  
  	case I2C_SMBUS_WORD_DATA:
  		wordp = stub_get_wordp(chip, command);
  		if (read_write == I2C_SMBUS_WRITE) {
  			*wordp = data->word;
  			dev_dbg(&adap->dev,
  				"smbus word data - addr 0x%02x, wrote 0x%04x at 0x%02x.
  ",
  				addr, data->word, command);
  		} else {
  			data->word = *wordp;
  			dev_dbg(&adap->dev,
  				"smbus word data - addr 0x%02x, read  0x%04x at 0x%02x.
  ",
  				addr, data->word, command);
  		}
  
  		ret = 0;
  		break;
  
  	case I2C_SMBUS_I2C_BLOCK_DATA:
  		/*
  		 * We ignore banks here, because banked chips don't use I2C
  		 * block transfers
  		 */
  		if (data->block[0] > 256 - command)	/* Avoid overrun */
  			data->block[0] = 256 - command;
  		len = data->block[0];
  		if (read_write == I2C_SMBUS_WRITE) {
  			for (i = 0; i < len; i++) {
  				chip->words[command + i] &= 0xff00;
  				chip->words[command + i] |= data->block[1 + i];
  			}
  			dev_dbg(&adap->dev,
  				"i2c block data - addr 0x%02x, wrote %d bytes at 0x%02x.
  ",
  				addr, len, command);
  		} else {
  			for (i = 0; i < len; i++) {
  				data->block[1 + i] =
  					chip->words[command + i] & 0xff;
  			}
  			dev_dbg(&adap->dev,
  				"i2c block data - addr 0x%02x, read  %d bytes at 0x%02x.
  ",
  				addr, len, command);
  		}
  
  		ret = 0;
  		break;
  
  	case I2C_SMBUS_BLOCK_DATA:
  		/*
  		 * We ignore banks here, because chips typically don't use both
  		 * banks and SMBus block transfers
  		 */
  		b = stub_find_block(&adap->dev, chip, command, false);
  		if (read_write == I2C_SMBUS_WRITE) {
  			len = data->block[0];
  			if (len == 0 || len > I2C_SMBUS_BLOCK_MAX) {
  				ret = -EINVAL;
  				break;
  			}
  			if (b == NULL) {
  				b = stub_find_block(&adap->dev, chip, command,
  						    true);
  				if (b == NULL) {
  					ret = -ENOMEM;
  					break;
  				}
  			}
  			/* Largest write sets read block length */
  			if (len > b->len)
  				b->len = len;
  			for (i = 0; i < len; i++)
  				b->block[i] = data->block[i + 1];
  			/* update for byte and word commands */
  			chip->words[command] = (b->block[0] << 8) | b->len;
  			dev_dbg(&adap->dev,
  				"smbus block data - addr 0x%02x, wrote %d bytes at 0x%02x.
  ",
  				addr, len, command);
  		} else {
  			if (b == NULL) {
  				dev_dbg(&adap->dev,
  					"SMBus block read command without prior block write not supported
  ");
  				ret = -EOPNOTSUPP;
  				break;
  			}
  			len = b->len;
  			data->block[0] = len;
  			for (i = 0; i < len; i++)
  				data->block[i + 1] = b->block[i];
  			dev_dbg(&adap->dev,
  				"smbus block data - addr 0x%02x, read  %d bytes at 0x%02x.
  ",
  				addr, len, command);
  		}
  
  		ret = 0;
  		break;
  
  	default:
  		dev_dbg(&adap->dev, "Unsupported I2C/SMBus command
  ");
  		ret = -EOPNOTSUPP;
  		break;
  	} /* switch (size) */
  
  	return ret;
  }
  
  static u32 stub_func(struct i2c_adapter *adapter)
  {
  	return STUB_FUNC_ALL & functionality;
  }
  
  static const struct i2c_algorithm smbus_algorithm = {
  	.functionality	= stub_func,
  	.smbus_xfer	= stub_xfer,
  };
  
  static struct i2c_adapter stub_adapter = {
  	.owner		= THIS_MODULE,
  	.class		= I2C_CLASS_HWMON | I2C_CLASS_SPD,
  	.algo		= &smbus_algorithm,
  	.name		= "SMBus stub driver",
  };
  
  static int __init i2c_stub_allocate_banks(int i)
  {
  	struct stub_chip *chip = stub_chips + i;
  
  	chip->bank_reg = bank_reg[i];
  	chip->bank_start = bank_start[i];
  	chip->bank_end = bank_end[i];
  	chip->bank_size = bank_end[i] - bank_start[i] + 1;
  
  	/* We assume that all bits in the mask are contiguous */
  	chip->bank_mask = bank_mask[i];
  	while (!(chip->bank_mask & 1)) {
  		chip->bank_shift++;
  		chip->bank_mask >>= 1;
  	}
  
  	chip->bank_words = kzalloc(chip->bank_mask * chip->bank_size *
  				   sizeof(u16), GFP_KERNEL);
  	if (!chip->bank_words)
  		return -ENOMEM;
  
  	pr_debug("i2c-stub: Allocated %u banks of %u words each (registers 0x%02x to 0x%02x)
  ",
  		 chip->bank_mask, chip->bank_size, chip->bank_start,
  		 chip->bank_end);
  
  	return 0;
  }
  
  static void i2c_stub_free(void)
  {
  	int i;
  
  	for (i = 0; i < stub_chips_nr; i++)
  		kfree(stub_chips[i].bank_words);
  	kfree(stub_chips);
  }
  
  static int __init i2c_stub_init(void)
  {
  	int i, ret;
  
  	if (!chip_addr[0]) {
  		pr_err("i2c-stub: Please specify a chip address
  ");
  		return -ENODEV;
  	}
  
  	for (i = 0; i < MAX_CHIPS && chip_addr[i]; i++) {
  		if (chip_addr[i] < 0x03 || chip_addr[i] > 0x77) {
  			pr_err("i2c-stub: Invalid chip address 0x%02x
  ",
  			       chip_addr[i]);
  			return -EINVAL;
  		}
  
  		pr_info("i2c-stub: Virtual chip at 0x%02x
  ", chip_addr[i]);
  	}
  
  	/* Allocate memory for all chips at once */
  	stub_chips_nr = i;
  	stub_chips = kcalloc(stub_chips_nr, sizeof(struct stub_chip),
  			     GFP_KERNEL);
  	if (!stub_chips) {
  		pr_err("i2c-stub: Out of memory
  ");
  		return -ENOMEM;
  	}
  	for (i = 0; i < stub_chips_nr; i++) {
  		INIT_LIST_HEAD(&stub_chips[i].smbus_blocks);
  
  		/* Allocate extra memory for banked register ranges */
  		if (bank_mask[i]) {
  			ret = i2c_stub_allocate_banks(i);
  			if (ret)
  				goto fail_free;
  		}
  	}
  
  	ret = i2c_add_adapter(&stub_adapter);
  	if (ret)
  		goto fail_free;
  
  	return 0;
  
   fail_free:
  	i2c_stub_free();
  	return ret;
  }
  
  static void __exit i2c_stub_exit(void)
  {
  	i2c_del_adapter(&stub_adapter);
  	i2c_stub_free();
  }
  
  MODULE_AUTHOR("Mark M. Hoffman <mhoffman@lightlink.com>");
  MODULE_DESCRIPTION("I2C stub driver");
  MODULE_LICENSE("GPL");
  
  module_init(i2c_stub_init);
  module_exit(i2c_stub_exit);